A variety of solid raw materials are commonly extracted with aqueous solvents, such as hot water, to form consumable aqueous extracts for use in foods, fragrances, or beverages. Common materials include roasted ground coffee, tea, and cocoa just to name a few. Typical and representative of currently employed methods and systems for performing such extractions are those used for brewing and extracting roasted coffee. Generally the prior art systems fall into two broad categories: small-scale home or commercial brewing equipment for producing beverages; and large-scale industrial extractors for producing concentrated extracts for use as flavorings or as raw materials for the production of instant coffee products. When used for the production of instant coffee products, the aqueous solvent is typically removed from the dissolved coffee solids by processes such as freeze drying or spray drying.
Typical prior art large-scale coffee extractors and associated extraction methods, especially when used to produce coffee extracts for the subsequent production of instant coffee, are designed to maximize the yield of soluble coffee solids in the extract from a given quantity of ground roasted coffee. This is done for economic reasons: the more soluble coffee solids extracted from a given quantity of roasted coffee raw material, the greater the quantity of final instant coffee product derived upon removal of the water. To this end, typical prior art large-scale coffee extractors are designed for the exhaustive extraction of typically low-grade ground coffee and not for production of a high quality, flavorful, fragrant extract. Many typical prior art extractor systems of this type employ one or more columns having fixed beds of ground roasted coffee. Representative of such a system is the one described in U.S. Pat. No. 3,830,940 to Sivetz. Many prior art systems employ circulation of hot water through the columns where the water flows into the bottom of each column and exits from the top, thus tending to expand and agitate the bed. Very hot extraction water, often in excess of 160 degrees C, is often fed to the column containing the most spent coffee (the coffee that has had the most solids already extracted) in order to thermally hydrolyze the coffee to enable extraction of additional solids, which are essentially free of flavor and fragrance. Often, the extract may be recycled through the columns to further increase the extent of the extraction of the ground roasted coffee. While such systems and methods are useful for exhaustive extraction, they are not ideally suited for producing high quality coffee extracts with desirable sweetness and flavor characteristics. The relatively long extraction times (for example greater than 1 hour), high water temperatures, and levels of dilution used in certain prior art extraction processes can result in extracts having a relatively high concentration of components that are bitter or have poor flavor characteristics, which are often passed on to the dried instant coffee products produced from such extracts. Many of the concentrated coffee extracts commonly employed as flavor components in the food industry (e.g. as flavorings for coffee ice cream, iced coffee beverages, and coffee syrups) are produced by reconstituting such poor quality instant coffee products with water or other materials.
It is understood that sweeter and more flavorful coffee extract can be produced near the beginning of an extraction cycle, when the fresh ground coffee has been in contact for a relatively short period of time with only a relatively small quantity of water, than can be produced later in the extraction process after the coffee has been exposed to additional quantities of water and more exhaustive extraction. Attempts have been made to improve upon the quality and flavor of coffee extracts and instant coffee products produced by large scale extraction processes. One such method described in U.S. Pat. No. 4,534,985 to Gasuu ('985) discloses an industrial scale continuous extraction process and apparatus for the extraction of coffee or tea. The apparatus involves a complex system using a number of extractant beds and extraction zones, where the beds are movable between zones by rotation of the apparatus. The process reduces the total time of the extraction process when compared to more conventional prior art extraction methods. The '985 patent also discloses the use of compressed air or an inert gas in a "recovery station" of the apparatus to maximize recovery of the residual liquid present in the spent grounds after extraction.
Various smaller scale brewing/extraction methods for home or commercial use are known in the prior art for producing beverages from solid raw materials such as coffee, tea and cocoa. Common methods include steeping or infusion in a static volume of hot water (i.e. steeping a tea bag in a cup of hot water), steam-driven percolation, and extraction via a continuous flow of hot water under the force of gravity through a bed of solid extractable material, typically coffee. The latter method described is the one typically employed in home "drip method" coffee makers. All of these methods typically produce a relatively dilute beverage-strength extract (typically, 1 lb of ground, roasted coffee will yield about 320 oz. of beverage-strength extract). In addition, because of the continuous addition of water used to drive the flow of extract through the bed, the beverages produced can contain undesirable quantities of bitter or off-flavor components.
An improvement to most of the above described methods for producing a sweeter, more flavorful, more fragrant, and more concentrated coffee beverage is the espresso method of coffee extraction. The espresso method of extraction typically employs a small-scale home or commercial brewing apparatus utilizing a less exhaustive extraction method to produce a relatively sweet, more concentrated beverage. Typically, a higher ratio of ground coffee to hot water is employed, for example about 1 lb. of ground roasted coffee may typically yield about 6-128 oz of coffee beverage. In order to allow sufficient contact time between water and the ground coffee, the method typically utilizes a finely ground coffee (e.g. 14 gram weight) with hot water being forced through the bed of grounds contained in the brew chamber by additional pressurized hot water. Most typical currently employed espresso type extraction devices are capable of producing only relatively small quantities of extract during each extraction cycle. In addition the quality of the beverage can be very dependant on the grind and packing of the coffee, which dictates the back pressure developed by the flowing water during the extraction, and the extraction time for a given total volume of beverage. A lack of control over these variables can lead to a poor or inconsistent quality of extract. Also, since hot water is typically used to force extract from the bed of ground coffee during the entire extraction process, an undesirable level of extraction may still occur, yielding an extract which is too dilute, and not ideally suited for use as a food or flavor additive without a subsequent, undesirable removal of excess aqueous solvent from the extract.
A variety of small-scale espresso style coffee brewers have been described which attempt to improve upon the performance of conventional espresso brewers. U.S. Pat. No. 5,127,318 to Selby ('318) and U.S. Pat. No. 5,473,973 to Cortese ('973) both disclose an apparatus and process for extracting espresso type coffee in which the pressure within the extraction region is regulated by a biased valving arrangement on the outlet line downstream of the coffee bed. The valves are designed to remain closed during the initial pressurization of the extraction chamber by hot water until a preset pressure is reached that can overcome the bias of the regulating valve. When such pressure is reached, the valve opens for flow and maintains a relatively constant pressure in the extraction chamber during the remainder of the extraction process relatively independent of the grind or packing of the coffee. In the disclosed systems, the pressure constantly rises until a predetermined pressure is reached, at which point, flow immediately commences.
U.S. Pat. No. 5,267,506 to Cai ('506) discloses an apparatus for automatically brewing espresso coffee and includes one embodiment where pressurized steam generated by a heating unit is passed through the coffee grounds to purge liquid so that the grounds will not drip when the brew chamber is removed.
U.S. Pat. No. 5,337,652 to Fischer et al. ('652) discloses an espresso machine and method utilizing a biased pressure relief valve down stream of the brewing chamber similar to U.S. Pat. No. 5,127,318 ('318) and U.S. Pat. No. 5,473,973 ('973) described above. The biased valve prevents flow from leaving the discharge line until the pressure within the chamber rises to a fixed predetermined level; immediately thereafter, the valve opens and maintains a relatively constant pressure within the brew chamber during the remainder of the extraction. The '652 system also includes an air pump with an outlet line in fluid communication with the water heating chamber. The air pump is used at the end of the brewing cycle to pump air through the coffee grounds in order to dry the coffee and produce a foamy head. The air from the pump is directed to the brewing chamber from the hot water compartment via a relatively complex automated valving/switching mechanism on a flow control manifold located within the water heating chamber. The air supplied to the brewing chamber in the '652 system passes through the water heating chamber before entering the brewing chamber thus adding heat and moisture to the gas. The '652 system is a relatively low pressure system with a maximum operating pressure disclosed of about 3.5 bar (about 50 psi).
While some of the above cited systems and methods for producing consumable extracts from solid raw materials represent, in some cases, useful contributions to the art of producing consumable extracts, there exists a need for improved methods and systems for producing variable quantities, including large volumes, of consumable extracts, including highly concentrated extracts, from solid raw materials, the extracts having desirable sweetness, flavor, and fragrance characteristics.